"Overlaid" plywood panels are manufactured by affixing sheet(s) of resin-impregnated fibre overlay paper to one, or both, sides of a plywood panel to impart a smooth surface to the finished panel. Overlaid plywood has a number of end uses including use in concrete formwork (where the paper overlaid side of the panel is positioned against a curing concrete surface to impart a smooth finish to the cured concrete); use in doors, liners, decks, siding or furniture surfaces where durable, paintable surfaces are desired; use in signwork (the paintable, overlay paper provides a surface which retains its smoothness and durability over time in exterior uses), etc.
Smooth, durable overlaid panel surfaces may only be produced if the plywood panel surface veneer underlying the overlay paper is smooth and free of defects. Surface variations as small as 0.008 inches may result in areas of low pressure to which overlay paper will not properly bond. It is therefore important, in the manufacture of overlaid plywood, to repair naturally occurring or man-made veneer surface defects. Such defects may include open knot holes, splits, holes made by worms or insects, pitch pockets, bark pockets, veneer roughness, chipped or solid knots, lathe marks, veneer shelling, impressions and splits and tears caused by handling or transport of the panels.
The present invention provides an improved method of making overlaid plywood in which panel surface defects are filled with a thermosetting resin before a sheet of resin-impregnated overlay paper is applied to the panel surface(s). (Either, or both, surfaces of a plywood panel may be overlaid in accordance with the invention.) The panel is then compressed and heated, thereby curing the gluelines on the plywood veneer and on the overlay paper and also thereby flattening and hardening the resin filler to form solid patches which are securely bonded to the overlay paper and to the underlying veneer and veneer glueline to produce a smooth-surfaced overlaid plywood panel.